1. Field of the Invention
The invention relates to an injection nozzle for use in a pressure-controlled fuel injection system for an internal combustion engine.
2. Description of the Prior Art
For the sake of better comprehension of the description and claims, several terms will now be explained: The fuel injection system of the invention is embodied as pressure-controlled. Within the context of the invention, the term pressure-controlled fuel injection system will be understood to mean that as a result of the fuel pressure prevailing in the nozzle chamber of an injection nozzle, a nozzle needle is moved counter to the action of a closing force (spring), so that the injection opening is uncovered for an injection of the fuel out of the nozzle chamber into the cylinder. The pressure at which fuel emerges from the nozzle chamber into a cylinder of an internal combustion engine is called the injection pressure, while the term system pressure is understood to mean the pressure at which fuel is available or is held in reserve within the fuel injection system. Fuel metering means furnishing a defined fuel quantity for injection. The term leakage is understood to mean a quantity of fuel that occurs in operation of the fuel injection system (for instance, a guide leakage), and that is not used for injection and is returned to the fuel tank. The pressure level of this leakage can have a standing pressure, and the fuel is then depressurized to the pressure level of the fuel tank.
In common rail systems, the injection pressure can be adapted to load and rpm. To reduce noise, a preinjection is often performed then. To reduce emissions, a pressure-controlled injection is known to be favorable.
Using a 2/2-way valve for triggering the injection nozzle is known from German Patent Disclosure DE 196 23 211 A1.
It is also known to employ a so-called varioregister nozzle in cam-driven systems. This injection nozzle with a reversible two-stage injection port cross section has until now been triggered via a pressure-controlled fuel injection system with a 3/2-way valve or with a cam-driven injection system.
To reduce the costs of producing a fuel system, especially for small engines, an injection nozzle according to the invention uses only a single 2/2-way valve as a metering valve per cylinder. The design becomes more compact, because functions such as valve opening and hydraulically-reinforced opening and closure are integrated with the injection nozzle. A force-balanced construction of the nozzle needle of the varioregister nozzle is possible. In hydraulically reinforced opening of the nozzle needle, the injection nozzle opens as far as a stroke stop. The stroke stop can be embodied purely hydraulically or hydraulically-mechanically.
Triggering the injection nozzle can be employed both for injection nozzles opening in the direction of the injection chamber and those opening in the opposite direction. To that end, the throttles in the control chamber, and the control chamber itself and the piston, merely need to be adapted in a structurally simple way.
If the leakage line is used to trigger the hydraulic or hydraulic-mechanical stroke stop, a hydraulic connection to the injection nozzle can be omitted. The leakage line is dammed up to a higher pressure by means of one or more valves and suitable throttling or pressure maintenance valves. Preferably, a control unit in the leakage line should be used simultaneously for all the cylinders.
If the injection nozzle is embodied by a varioregister nozzle, instead of by a seat-type or blind-bore nozzle, then the course of injection can be adapted even better to the requirements of the engine.